Typically, covers for the fronts of motor vehicles, especially Porsches, are made out of a flexible plastic material such as vinyl or, for true luxury, they are made out of leather. In either instance, because the cover is flexible, naturally it cannot provide the resistance from dings and dents from rocks flying off the roadway surface that a rigid shield could provide.
Additionally, especially with the leather models, the contact of the surface of the cover actually leaches and discolors the finish on the vehicle.
Even with these drawbacks, however, the prevailing use of the flexible "bra" for the front end of a sports car stands testimony to the desireability of protecting that part of the vehicle which takes most of the abuse from roadway objects and airborne particles. There is a need, however, for a "bra" that offers even a greater degree of protection, and does not directly contact the finish of the car in most places, and thus does not leach the finish.